1. Technical Field
The present invention relates to a printer and a printing method.
2. Related Art
A printer carries out printing by expelling a jet of ink from a nozzle so that ink droplets (dots) adhere to a medium (roll paper). Another type of printer has a roll paper printing mechanism that appropriately feeds a medium from paper wound in a roll shape (roll paper) by an amount required for printing and carries out printing. During printing, these types of printers adjust an amount by which the medium is transported by controlling an amount by which roll paper is rotated and an amount by which a transport roller that transports the medium (paper) fed from roll paper is rotated.
A printer having a roll paper printing mechanism controls the amounts of roll paper rotation and roller rotation so that a certain tension is applied to the medium to prevent the medium from slackening while the medium is being transported. Since the medium is consumed as printing proceeds and the roll diameter of the roll paper is reduced, however, the amount of roll paper rotation is not correctly controlled. Accordingly, it has been difficult to constantly apply a certain tension to the medium being printed.
To solve the above problem, a method has been proposed in which the amount of roll paper rotation is adjusted by controlling the torque setting of a motor that drives roll paper in correspondence with a change in the roll diameter, enabling a certain tension to be constantly applied to the medium (see JP-A-2009-208921, for example).
In the method in JP-A-2009-208921, an inertia generated due to the rotation of roll paper during printing is not considered. When roll paper with a large roll diameter is used in a large printer for business use or the like, for example, a large inertia is generated accordingly. If the large inertia is applied during the control of the roll paper driving motor or transport roller, response characteristics are worsened in acceleration and deceleration of the motor or the like and control precision is lowered. Since, in particular, the transport roller needs to repeatedly control the transport and stop of the medium being printed, if the operation of the transport roller is affected by the inertia, it becomes difficult to precisely transport the medium.